1. Field of the Invention
The present invention generally relates to the fabrication of non-planar semiconductors, and more particularly to a method for bonding single crystal membranes to a curved surface and relieving the lattice stress in the membranes due to formation of quantum wires of a dissimilar element.
1. Discussion of Related Art
In the microelectronic industry, integrated circuitry is typically fabricated on the surface of a flat single-crystal silicon wafer, generally known as a substrate, for use in microelectronic devices. Quality and characteristics of these microelectronic devices are altered by quality and characteristics of the substrate. In particular, material purity, dislocation density, and level of lattice strain effect the behavior and performance of these devices. Additionally, the introduction of well controlled strain facilitates band-gap engineering and has led to the development of new devices, such as SiGe heterojunction bipolar transistors (HBT's), among others. Another trend in device engineering is associated with developing technology capable of producing low-dimensional structures, such as quantum wells, quantum wires and quantum dots.
Process induced lattice stress (as a result of oxidation, doping, ion implantation, silicidation, etc.) combined with the intrinsic silicon wafer dislocation density may significantly degrade device performance reliability. U.S. Pat. No. 4,769,689 discloses relieving the stress and resultant warping caused by lattice mismatch by doping germanium on an initial silicon crystal layer which consequently maintains the wafer in a flat configuration.
U.S. Pat. No. 5,546,417 discloses a basic semiconductor element having electronic circuitry fabricated on the surface of a non-planar substrate. The required non-planar nature of the basic semiconductor element assembly creates difficulties when integrating the silicon membrane with the non-planar supporting structure because stress may occur within the silicon lattice if the surface area of the supporting structure is a cylinder or cone having a small radius of curvature.
Furthermore, a high quality bond between the semiconductor material and the supporting structure is required. However, a problem arises while attempting to bond a flat silicon membrane to a non-planar supporting structure which has a small radius of curvature due to stress build-up within the membrane followed by lattice relaxation and resultant nucleation of dislocations. Such behavior prevents production of a semiconductor material having a sufficiently high quality for use in certain applications. Another challenge is in achieving a high quality bond between the supporting structure and a single crystal membrane.
Accordingly, it is an object of the present invention to provide a method of fabricating a substrate for a basic semiconductor element which overcomes these and other shortcomings in the prior art.